Accumulating evidence indicates that specific cognitive deficits may be present several years prior to an initial clinical diagnosis in individuals who later develop Alzheimer's disease (AD). In particular, recent research examining specific components of attentional control systems may be potential early cognitive markers for AD. For example, deficits in spatial controlled attention, working memory, and prospective memory have been shown in healthy middle-aged adults, who have the ApoE e-4 gene compared to individuals who do not have the e-4 allele, even though these individuals do not produce deficits on more standard neuropsychological measures. There have not been any studies that have attempted to decompose the hypothesized theoretical components of attentional processing (maintenance, selection, switching, and divided attention) presumed to be deficient in early stage AD. Moreover, there is little evidence that the underlying components of attention are consistent within an individual across different attentional measures and across different testing sessions. The goal of the present proposal is to target specific components of attention, and provide individual attentional profiles in an attempt to identify early cognitive markers for Alzheimer's Disease. In addition, recent evidence suggests that components of attention may be differentially affected by distinct personality types, and that variability in behavior may be an important discriminator in early stage DAT. Hence, the proposed studies will also provide indices of personality and variability profiles. The proposed experiments will isolate four distinct components of attention: maintenance, selection, switching, and divided attention. Based on the extant literature, three experiments will be designed to tap each of the four components of attention, yielding a battery of 12 attentional tests. Two categories of individuals will be tested in this battery: individuals who have a biologic parent with DAT and control individuals who do not have a biologic parent with DAT. Within each of these two categories, 3 age groups will be included (ages 45-54 years;55-64 years;65-74 years). Approximately 120 subjects per category (40 per age group within each category) will be tested in the first wave of experiments. We anticipate that 70% of the total sample will be tested beginning in year four for a second wave. The goal of these multiple tests will be to provide a replication of the factor structure, and also to index the consistency of the within-subject profiles. Analyses will be conducted to determine the relation between the attentional, personality, and variability profiles of the individuals and the biomarkers from the remaining Projects, along with APOe4 status of the individuals.